Maintain Your BalanceA simple wheel balance will cure most vibrations. But if that doesn't cure the problem--or if it cropped up suddenly within a reasonable time after a wheel balance--your problems may go deeper.

Begin by cranking the wheels over to the steering stop and looking at the inside of the rim. It's customary to split the amount of the balance weights between the inside and outside of the rim. If a weight (even an old one) has come off, that could be the problem. The weight should leave a clear outline, so you'll know exactly how much is missing. If the balance weight was added recently, you can take it back to the shop for a replacement.

Also inspect the rim--inside and outside--for any damage. Look for packed mud on the inside of the wheel. Also look at the tires--if you see any bulges or uneven wear of the tires, consider them in the "probable cause" category.

Nothing obvious? Take the car for a test drive. When the vibration occurs, is it while you're accelerating through a bend? That means it's both torque and speed sensitive. When you pull back to your garage, inspect the axle shafts, looking for damage to the boots. Constant velocity joints can wear out. But if the boots are intact, the clamps are holding them at each end, and there's been no loss of lubricant and no intrusion of road film, then they're probably in good condition.

If the vibration is not related to torque, shift into Neutral and let the vehicle coast at the problem speed. Still have the vibration? It's speed sensitive pure and simple. This could be the source of your troubles, even if the wheels are balanced and the tires are good. It's not a powertrain or driveline issue.

Keeping Your BearingsJack up the front wheels by the control arms, so they're off the ground, and support them with safety stands. Grasp each wheel, holding it first at the sides, then at the top and bottom. See if you can rock the wheel in and out and if you can feel any looseness, which indicates a loose wheel or worn wheel hub bearings. To replace wheel bearings on front-drive cars, you've got to remove the wheel hub. This job requires a slide-hammer puller, a tool typically available from the rental Peg-Board of many auto parts stores, and a torque wrench capable of the high torque usually required for the retaining nut (often well over 200 ft.-lb.). Front-drive wheel bearings (and the front bearings on many rear-drive cars) are well-sealed and often are life-of-the-car without lubrication. However, if you've been on a lot of secondary roads, or glanced off a curb hard enough to bend a rim, they could be worn or damaged.

If you have a rear-drive car it probably has adjustable front wheel bearings, and finding a lot of free play in these is not surprising. To adjust, remove the cotter pin, tighten the wheel bearing nut to about 20 ft.-lb. to seat the bearings, and back off so they're just free but have so little play that you really can't feel it. Then line up the slot in the spindle with the nut and insert a new cotter pin.

Steering Your Way

You may not feel free play in a front wheel (front- or rear-drive), but try rocking it in and out with a bit more effort, but not enough to move the steering linkage. That could demonstrate free play from wear in the tie-rod ends or ball joints. If you're not sure where the free play is, pry up on the bottom of the tire and watch the ball joint to see if it has free play1/4 in. is a lot.

To check a tie-rod end joint for looseness, try to flex it by hand. A good tie-rod end should feel snug, but not immobile or stiff.

On rack-and-pinion steering, it's a good idea to check the tie rods' inner sockets. They're covered by the steering rack boots, but you can squeeze the boots to hold the inner joint. Jack up the front end to take the weight off the front wheels. Have a friend slowly turn the steering wheel a partial turn to each side, while you feel for looseness.

Look Out For RunoutJust because you can't feel a lot of free play or "wobble" in a wheel doesn't mean there isn't enough to cause vibration. It doesn't take a lot to be responsible for objectionable vibration at speeds of 60 to 70 mph and aboveany deviation from a truly circular spin is called runout. It can be vertical (up-down) or horizontal (in-out).

The only practical way to check for runoutfront or rearis with a dial indicator, another tool you can rent at many parts stores. There are several different checks to make to pinpoint the source of the runout.

Mount the indicator on something heavy that won't move, such as an anchor plate or wheel hub/knuckle. Position the plunger for the specific runout check. Example: For a radial runout test, rest it against a good tire tread groove. Slowly turn the tire and measure the amount of runout, ignoring jumps in the plunger that result from the shape of the tread or minor imperfections in it. If there are factory specifications for runout, use those.

If you don't have specs, see if the runout is about .050 to .060 in.this measurement is considered rule of thumb. The tire almost surely isn't the issue, although there is precision equipment that can check a tire for heavy spots. We knowyou don't have it and can't rent it. Most professionals don't have it either, which tells you how common it is.

To isolate the source of the runout, check it at the wheel with the plunger on an underside horizontal surface. Ignore minor imperfections in the wheel finish (paint, weld, tiny dings) that cause the plunger to jump instantaneously. If the runout is over .045 in., the wheel should be replaced.

If radial runout isn't bad, check lateral runout with the plunger against the sidewall, even if the in-out rocking didn't show anything. Obviously, ignore any plunger movement from raised lettering, etc. If the runout is over .045 in., it's too much. Here again, isolate the runout by checking at the wheel with the plunger against a vertical surface. The rule-of-thumb specs are the same as for radial runout.

When the runout at the wheel is excessive, a new wheel normally is the answer, but not always. Remove the wheel and check runout on the wheel hub. Making a lateral runout check is an obvious procedure because there's a hub face against which you can rest the plunger.

For a radial check, it may be more difficult if the top surface of the hub isn't reasonably smooth because you have to use the threaded edges of the studs, and, typically, there are only four or five of those studs. So it does take some careful measuring to see if there's a significant amount. You have to look for the peak reading at each stud to be sure you're measuring at the outermost point. Unless almost all the radial runout is in the bolt circle, and that amount is at least .030 in., go for a new wheel. Replacing the hub and bearing on a front-drive is not a quick and easy job.

It can take a couple of hours to check out the possible causes of high-speed vibration, and you may be tempted to take the car in for wheel alignment to see if that helps before you spend time on all these other things. Sorry. Unless there's some evidence of wheel misalignment (such as irregular tire wear), a wheel alignment is not going to help at all. In fact, until you first isolate and correct the cause of the vibration, alignment would be a waste of time and money.

Remove the cotter pin to retorque a loose front wheel bearing on a rear-drive car.

Total radial runout at the tire tread should be no more than .050 to .060 in.

If radial or lateral runout is high, check both runouts at the hub to rule out a bent rim.

MORE INFORMATION:

TIRE & WHEEL MARKINGS:
There are marks that the tire and wheel manufacturers use so as to align the "high" and "low" spot of the wheel/tire combo. (BTW, any good shop will know this).

The valve stem hole is drilled in the geometrically "low" spot of the rim (ie the smallest diameter, within manufacturing tolerances) by the wheel manufacturer. The tire manufacturer, in turn, marks on the wheel the radically stiffest part of the tire (which is effectively the "highest" spot) with a color spot or other label. Aligning these two, the spot and the valve stem hole, is called Match Mounting which is intended to give the smoothest drive possible.

WHEEL MOUNTING:
Wheels can be aligned with the hub in two ways: either thru their lug nuts or via the hub-centric or center pilot of the wheel. Yes, that center hole in the back of a wheel is what aligns the center of the wheel to the center of the hub.

VIBRATIONS WHILE DRIVING:
As a rule of thumb: vibrations felt under 40mph are related to runout. Most vibrations of this nature are caused after hitting bid/deep/large etc. objects; this is definitely cause and effect in action. If a vibration is felt at over 40mph it is usually related to balance.

OTHER TIPS:
Still having vibrations? Try having your free runout, both in the lateral and radial sense measured. Both the tire and the rim should be measured for lateral and radial runout. The shop manual calls for 0.080 in., but a better rule is not to exceed 0.060in for the lateral and radial runout. If your runout exceeds this number, you will have perceptible vibrations. Note that runout is first measured on the car, and if it exceeds it, then the wheel should be measured off the car to isolate the problem. Yes, the bearings in the hub could also have damaged by that last pothole and causing vibrations too. It also can be that the mounting surface of the hub has been damaged or is defective, or that the stud circle of the wheel may not be centered on the hub. and finally, check your steering rack mounts too - worn/loose mounts can add vibration to your steering wheel.

GETTING A GOOD WHEEL/TIRE BALANCING JOB DONE:
A good dynamic balancer should be checked so that it zero's itself before balancing the tire and after the weights are on the tire while the tire is on the machine.

If there is still a vibration, an on-car balance of the wheel should be done, which will balance all rotating part on that corner. This is usually used for fine tuning a dynamic balance, and not everyone has the equipment to do it. Note that if you rotate the tire after an on-car balance, it will have to be redone.

Other rules of thumb are that if it takes more than three ounces to balance a tire, you will be better off getting a different tire or wheel.

If a recent vibration is felt, check to see that a weight has not been lost when hitting a pothole.

NEED FOR ACCURACY:
Most dynamic wheel balancers that shops use are accurate to 0.25 oz. (or about what a quarter weights) ..this would generate a force of about half a pound at 65mph for a 24inch diameter tire. This accuracy used to be enough and the forces generated were not notices in the days of rear wheel drive cars with long arm suspensions and parallelogram power-assisted steering. But on modern cars, it would be totally unacceptable. There is a new “European” accuracy standard which calls for an accuracy rate of plus or minus one gram (that's 0.035 oz.!).

Some of the newest balancers can come close to this standard with an accuracy of 0.05 oz. - which is five times better than the balancer accurate to 0.025 oz.

Some of these new balancers also allow for special modes so that the balance can be calculated with the weights on the inside; "patch balance" modes which allows for a weight "patch" to be mounted inside the tire when a lot of weight is needed to balance the tire (note that this is very specialized and hard to find machine); match mounting of the wheel and tire is supported on some machines; others allow for "split weight" modes so that two smaller weights can be used or when construction impeded mounting of a weight (note that this increases accuracy by eliminating the rounding error that sometimes occurs when a single large weight is used). Even the mounting of the wheel to the machine can be specialized with horizontal mounts, hydraulic collets, etc.

OTHER THINGS TO CHECK:
Things that do not affect the dynamic balance of the wheels are: tire alignment, warped rotors (they will make the pedal pulse when brakes are applied and simultaneously make the steering wheel vibrate back and forth for really bad ones - otherwise they do not affect the dynamic balance of the axle) Worn out ball joints, shocks, bushings and tie rods can introduce vibrations that will feel like an out of balance condition.

PROPERLY TORQUING DOWN THE WHEELS:
Finally for those warping your rotors, skip the impact wrench and try mounting your wheels with a torque wrench using 70-80 ft-lbs of torque. Even and equal torque on all lug nuts will prevent warping of rotors 9with a possible exception being cross drilled rotors).